Magnetically operated float switch



DeC- 6, 1955 1 P. HANSON ET A1.

MAGNETICALLY OPERATED FLOAT SWITCH 4 Sheetgfsheet l Filed June 22 1953Dec. 6, 1955 L. P. HANSON ET A1.

MAGNETICALLY OPERATED FLOAT SWITCH 4 Sheets-Sheet 2 Filed June 22, 1953N O S N A H R U O L HowARD H. susKm INVENTORS De 6, 1955 1 P. HANsoNr-:T AL` 2,726,296

MAGNETICALLY OPERATED FLOAT SWITCH Filed June 22, 1955 4 Sheets-Sheet 342 Y 4o 43 f FIG 5 `l uuml mmm 56 Yll 6| mlb /49 LOUIS P. HANSON HOWARDH. SUSKI N INVENToRs Dec. 6, 1955 L. P. HANSON ET A1. 2,725,296

MAGNETICALLY OPERATED FLOAT SWITCH Filed June 2.2, 1955 4 sheets-sheet 4LOUIS P. HANSON HOWARD H. SUSKIN INVENToRs 2,726,296 Patented Dec. 6,1955 MAGNETICALLY OPERATED FLQAT SWITCH Louis P. Hanson and Howard H.Suskin, Seattle, Wash.

Application June 22, 1953, Serial No. 363,285

8 Claims. (Cl. 20G-84) This present invention relates to the general artof enclosed electrical switches and more particularly to a switchintended for use in an aircraft fuel system for controlling, orindicating, specified fuel levels. The switch is characterized byproviding in an hermetically sealed compartment, a permanent magnet andtwin armatures adapted to sequentially make or break an electriccircuit. The actuating means is a soft iron core, having a barrelshape,reciprocating in a tube having an opening externally of the switchcompartment and which core is actuated by a cork-type float. The softiron barrel-shaped core directs a magnetic circuit from a permanentmagnet through two soft iron armatures which armatures in turn, actuatethe electrical contacts.

This present magnetically operated iioat switch overcomes many ot' thedeficiencies experienced with float switches of the types previouslyused.- Aircraft operation calls for equipment that will assure certaintyof operation over long periods even though the mechanism is exposed to ahigh frequency vibratory environment. These severe operationalconditions have been met by isolating portions of the operatingmechanism by rubber mounting the same, by providing double-actingcounterbalanced armatures of considerable mass which operate theswitching mechanism without reliance upon springs and such devices. Byarranging the various parts so that vibration and friction can bereduced to a low level, the operational characteristics admit of longperiods of satisfactory functioning with an abundance of operationalenergy available to insure the functioning of the switching mechanismeven though it may have been at rest for long periods, thus a dependableswitching arrangement is provided which fully meets the requirements ofthe aircraft industry.

The principal object of this present invention therefore is to provide amagnetically operated float switch for use in an aircraft fuel systemfor controlling or indicating l into the hermetically sealed unit and isso arranged thatr the iron core never leaves the magnetic field of theunit.

A further object is the provision of ay dual toggle mechanism employingtwo armatures and which mechanism, in turn, avoids any dead centerposition of the switch contact members.

A further object of this invention is to provide a float switch whichcan be set to indicate either high or low level operational positions.

A further object of this invention is to provide a mechanism having suchan over abundance of lavailable energy that it will not be operationallyaffected by any normal loss of strength in the permanent magnet.

Further objects, advantages and capabilities will be apparent from thedescription and disclosure in the drawings, or may be comprehended orare inherent in the device.

In the drawings:

Figure l is a vertical sectional view through a magnetically controlledfloat switch made after the teachings of this present invention;

Figure 2 is a fragmentary view in elevation, partly in section, showingthe armatures used in this equipment together with certain of theco-related parts;

Figure 3 is a perspective View, partly in section, illustrating the coremember used to control the flux iiow in this equipment;

Figure 4 is an exploded perspective view of the sealed housing togetherwith the parts normally disposed therein;

Figure 5 is a perspective view on an enlarged scale, showing theswitching unit;

Figure 6 is a perspective view illustrating one of the armaturesemployed in the switching unit;

Figures 7, 8 and 9 are diagrammatic views on an enlarged scale andpartly in section illustrating the sequential operation of the switchunit contact members;

Figures l0 and ll are diagrammatic perspective views illustrating themodification of the ux flow due to the difference in placement of themovable core associated with this switching unit.

Referring more particularly to the disclosure in the drawings, thenumeral 10 designates generally the housing which hermetically enclosesthe switching mechanism. This is provided with a mounting ange 12 havingsuitable mounting openings and an integral bottom plate 14, and an upperclosure plate 16 which is xedly secured in place, as by soldering, whenthe switch mechanism has been fully assembled, tested, and installed.Centrally disposed with respect to housing 10 is a core guide tube 17,of non-magnetic material, having a closed inner end and an open outerend. This tube completes the hermetic seal for the parts and alsoprovides a path for the soft iron plug or core 18 which is disposed forlimited reciprocation within the cylindrical cavity 20 provided by tube17; Core 18 is relieved as by grooves 19, to provide for fluid passagearound it. Secured to the outer periphery of the depending ring, formedas part of plate 14, is a float housing tube 22. Tube 22 is removablysecured to housing 10 as by a plurality of screws 23 and isconcentrically disposed with respect to cavity 2t) so that float 24 mayreciprocate therein. This tube is provided with a plurality of upperholes 21 and a similar set of holes 25 near its lower margin.

Float 24 which is preferably formed of resin impregnated cork is adaptedfor positioning upon an axially disposed tube 26 which tube also carriesthe iron core 18. It has been found desirable to employ a tube 26 andclosure 29, preferably of nylon, rather than a solid rod in order toprovide the requisite stiffness without excess weight. It is desirableto provide adjusting and securing means so that float 24 can beadjustably positioned on tube 26 as by threading the exterior of tube 26and provide a self-locking nut arrangement as 27. On the other hand itmay be desirable in certain installations to employ a smooth outersurface of tube 26 and a frictional locking means in lieu of the nut at27.

Adapted for locking upon tube 26 isa positioning diaphragm assembly 23.The periphery of diaphragm 28 is serrated or otherwise provided withfluid passageways but has as a prime object a plurality of bearingsurfaces adapted to engage the inner surface of tube 22 and thus providea guide means which will maintain tube 26 substantially axially alignedwith cavity 20. Considerations of friction and the movement of uidindicates that diaphragm 28 should not make too snug an engagement withtube 22 but be capable of some floating therein and in order that nobinding will occur on plug 18 the outer periphery of the same where itengages tube 27 is made barrel-shaped with minimum tolerances at thehorizontal central plane. This permits a small amount of displacementfor the bottom end of tube 26 without in any way building up frictionwhich would tend to lessen the workability of the unit. Float housingtube 22 is provided with a bottom closure member as 30 and is providedwith a tubing connector fitting 31.

Disposed within housing 10 are the various elements making up themagnetic switching mechanism, which components are generally shown inthe exploded View of Figure 4. These units consist essentially of thepermanent magnet 32, fixedly secured to housing 10 by means of aplurality of machine screws 34 and the coacting clamp bar 35. 'lhe twoends of magnet 32 are vibration insulated from the switch unit by beingenclosed in resilient covers of tray-like form 36.

Disposed within the path of the flux created by perma nent magnet 32 isthe switch unit 4t). This unit which is shown in various views,particularly in Figure 5 is i mounted upon tube 17. lt is very desirablehowever that the same be not xedly mounted and to this end the switchingunit 4t) is provided with a central bore 42 which encircles tube 17 withreasonable clearance. At each end of the assembly bore 42 iscounterbored as at 43 and 44 to accept respectively the resilient rings45 and 46. These resilient rings provide adequate cushioning to dampenout high frequency vibrations to a very low level, below that which hasany effect upon the workability of the unit.

The switching unit is mounted upon its own framework which as viewed inFigure 5 consisting of the two vertical frame portions 48 and 49 and thehorizontal portions of the same frame as 51 and 52. This open frameworkprovides for the exact positioning of the various coacting units whichare either secured thereto in a fixed relationship or pivotably securedeither to the frame or to the members which are fixedly secured to thisframework. Fixedly secured to the unit frame are end-bearing members 53and 54. These members have cut in them respectively the counterbores 43and 44 in which are seated the resilient washers 45 and 46 respectively.Fixedly secured to bearing members 53 and 54 are the soft iron bars 56and 57. These bars abut the ends of the permanent magnet 32 except forthe imposition of the resilient tray-like members 36, and are used toform part of the switching unit frame and at the same time cut down onthe air gap between the magnet 32 and armatures 60-61.

Pivotably disposed between frame portion 48 and bar 56 and frame portion49 and bar 57 respectively, are the balanced armatures 60 and 61, madeof soft iron. These armatures are iixedly mounted upon bearing members62 which pass through openings 64 in the armature members. Bearingmembers 62 are secured between the frame portions as 48 and 49 and theopposite bars 56 and 57 which are graphite film coated. To insure thatthe armatures will continue to operate upon the bearing members withoutface friction, a lock screw 65 is employed in the armature so as toposition the armature in a central position upon the pivot members. Theconstruction of the armatures themselves is probably best illustrated inFigure 6 in which it will be noted that there are two arcuate surfacesas 66 and 67 which are formed to a curve concentric to the outside oftube 17. Further it is to be noted that these two surfaces are not acommon one but are angularly disposed with respect to each other to theend that when the armature pivots about openings 64 each of the surfacesalternately will partially encircle but never come in contact with tube17. Each armature is further provided with a head portion 68 whichcounterbalances the weight of portions 66 and 67 and disposes the massof the same to present the same area in the magnetic field.

Fixedly secured to the armatures are the switch operlti ating bars 70and 71. The two bars are offset away from a plane of the armatures so asto pass around tube 17 and the construction is similar excepting thatone as 70 has a metal detent or post 72 while the other has a bifurcatedend 74, the opening of which is considerably greater than the diameterof detent 72. This serves a purpose to be stated later. Secured normallyto the outer side of arm 70 is the central contact member 73.

The bifurcated end 74 which is provided to engage detent 72 is designedto apply the pressure of bar 71 to the switch contact with manufacturinglimitations in mind. While it is possible to interlock the two bars 7i)and 71 by various means we have found it desirable to place theinterlocking detent 72 away from a plane intermediate the two armaturesand nearer armature 61 so as to avoid the central contact member 73.Since the angular movement of bars 70 and 71 are the same, the verticaltravel of detent 72 is less than a point on arm 71 which contacts detent72. Therefore a relatively wide slot 74 is provided to compensate forthis dilference in vertical travel while retaining iixed angularrelationship.

The horizontal bar portions 51 and 52 of the main switch unit frame haveoutwardly extending lug portions F6 and 78. To these lugs are tixedlysecured two point electrical contact members Si) and S2. Theconstruction of these members is best illustrated in Figure 5 and thethree Figures 7, 8 and 9. A U-shaped insulating washer arrangement isprovided at 84.

Soldering lugs as 75 and 85 are normally formed as part of contactmembers and 82 and to these are connected electrical conductors thatlead outside the case through glass bead insulators.

Method of operation After a float switch of this order is placed inservice, the switching mechanism is not available for adjustment orservicing. Consequently its various components must be fully testedbefore assembling. Prior to being placed in service for most purposesthe evacuation equipment is applied to an opening in cover 16 and whenevacuation has been completed, the chamber is filled with an inert gas,as dry nitrogen, and then sealed as by soldering the evacuation opening.There are certain uses when a suitable damping oil may be employedinstead of the inert gas. The next step to be completed before placingthe unit in service is to adjust the position of float 24 upon stem 26.The positioning will be determined by experience and will be differentfor a high or a low level operation. Certain conditions will dictate theover-all length of tube 22 and this in turn will call for a similarchange in the length of tube 26. In this operation it is very desirablethat the soft iron plug 18 be positioned within tube 17 and also withinthe limits of the armature plates 66 and 67. It therefore follows thatthe length of tube 22 will control the downward limit of the movement ofthe core 18 and should therefore be of the proper length to achieve thisdesired result. By insuring that the plug 18 never leaves the magneticeld, the armatures are at all times acted upon by a large magneticforce, which holds them in either the actuated or de-actuated position.No springs need be employed for this operation.

As viewed in Figure l the lower armature surfaces 66 are being actedupon by the increased flux lines passing through plug 18 and this force,through arms 70 and 71. move the central contact member 73 intoengagement with the two upper contacts forming part of member 80. Whenunder action of float 24, plug 18 is moved to the upper position opposedto the armature contact surfaces 67, both armatures pivot about theirpivot axis 64 so that surfaces 67 are in close proximity to tube 17.This action through arms 70 and 71 moves the centrally disposed contact73 downwardly to contact the lower contact member 82. It is to be notedthat the central contact member is one large contact surface suicient inextent so that the two spaced contact points 77-79 and 81-83 of eithermember 80 or 82 respectively can both engage this large central Contact.lt is desirable however that both Contact points of the same` Contactmember either 80 or S2 do not engage the central contact at the sametime. An optimum arrangement is where one point will contact followedshortly by the second contact of the same unit. This means that thecurrent starts to flow through a single contact point, more importanthowever, is the action when the current is broken. Members 80 and S2 areboth of resilient construction and like wise the two contact pointsbeing on separate prongs of the member also have a degree of resiliency.However, experience shows that the contact points, as 79 or 83, that rstengages the central contact will, because of the placement andresiliency of the metal, be the last one to leave. Therefore, it assumesthe full burden of the arcing incidental to breaking the circuit and asthis arcing continues from various making and breaking of the circuit,it is common to have a high electrically resistant carbon deposit builtup at this point. This is a desirable condition in that it means longerlife for the paired mating contact points, as '77 or 8l. The matingcontact point of the pair of a single contact member is of courseusually left clean of all carbon deposits as it has made contact afterthe initial contact has been made by the companion point and it leaves,or breaks its contact, before the carbonized point has broken thecontact and accepted the results of the arcing which normally ensues.The uncarbonized contacts 77 and 8l then offer a low resistance path forelectrical current How. The sequential operation of these members isprobably best shown in the three diagrammatic Figures 7, 8 and 9. lt isdesirable to point out that such niccties of operation are achieved onlyby a well balanced design which avoids the usual interference caused ifvibration is experienced by these parts, it then follows that thedesirable arrangement is one in which the mass of the magnet and itsassociated parts are entirely isolated from the switch unit as by meansof the resilient rings 45 and 46 and pads 36, rl`his is no doubt acontributing factor to the long life of these units and the certainty oftheir operation. The absence of high frequency vibration assured by theresilient mounting of the switching unit permits the smooth functioningof the double acting, counterbalanced armatures 69 and 6l and permitsthem to oscil late without interference on their respective pivots underurgence ot the ux flow from permanent magnet 32. The low frictionarmature pivot bearings 62 again contribute to the smooth functioning ofthis device and permit the L' functioning of the device even thoughafter long periods of use, the flux flow of the permanent magnet shouldbe greatly decreased. Et is further desirable to point out that a designof this order can be made in Small size and the components are such thatweight has been conserved to a remarkable degree, a very desirableattribute in a piece of equipment designed for airplane use. The outputof this device is carried through the central contact conductor 9% andthe two conductors 92 and 94 which are alternately energized to providecontrol circuits which find many uses in aircraft fuel systems forcontrolling or indicating specified fuel levels.

Another factor contributing to the certainty of operation is thecalculated balance of the forces applied by the float due to an increaseor decrease of liquid displacement and the attraction of the core bymagnet 32. The magnet tends to hold the core in place until the delayedmovement of the oat creates an overbalancing force which then takescontrol and gives a quick throw to the switch mechanism.

It is believed that it will be clearly apparent from the abovedescription and the disclosure in the drawings that the inventioncomprehends a novel construction of a magnetically operated iloatswitch.

Having thus disclosed the invention; we claim:

l. A magnetically operated oat switch, comprising: a hermetically sealedhousing adapted to house and iixedly support a bar magnet andresiliently support an electrical switching means; an axially disposedcylindrical cavity extending into said housing and open at its lowerend; a barrel-shaped iron core disposed for reciprocation within saidcavity and to thus change the path of the flux ow ofthe magnet; a liquidbuoyant oat disposed in substantial axial alignment below said core;means operatively and adjustably connecting said core and said lloat andenabling the oat to position the core within said cavity; means forguiding the lower end of said connecting means to maintain it insubstantial alignment with said cavity; an electrical switching meanshaving two opposed resiliently mounted, two contact switch members and amovable single contact switch member disposed between the resilientmembers; said bar magnet being arcuate in form to partially encirclesaid switching means; a pair of counterbalanced iron armatures, mountedon horizontalv pivots, and disposed in the iiux path of said magnet; anarm secured to each of said armatures and operatively connected to saidmovable single contact switch member; said armature having verticallyspaced, arcuate contact surfaces adapted to substantially contact theouter wall of said cavity, alternately, as said core is moved into thehorizontal plane of said contact surfaces; and vibration damping meansadapted to yieldably support the armature and switch members from saidhousing.

2. A magnetically operated Float switch, comprising: a hermeticallysealed housing adapted to house'and ixedly support a bar magnet andresiliently support an electrical switching means; an axially disposedcylindrical cavity vextending into said housing and open at its lowerend; a barrel shaped iron `core disposedfor reciprocation within saidcavity and to thus change the path ot the flux flow of the magnet; aliquid buoyant oat disposed in substantial axial alignment below saidcore; means operatively and adjustably connecting said core andy saidfloat and enabling the lloat to position the core within said cavity;means for guiding the lower end of said connecting means to maintain itin substantial alignment with said cavity; an electrical switching meanshaving two opposed, resilient, two Contact, switch mernbers and, amovable single contact switch member disposed between the resilientmembers; said bar magnet disposed to partially encircle said switchingmeans; a pair of counterbalanced iron armatures, mounted on horizontalpivots, and disposed in the lux path of said magnet; an arm secured toeach of said armatures, one arm having an outwardly extending detent andthe other having a bifurcated end adapted to engage the same, and tothus operatively connect the armatures to said movable single contactswitch member; said armature having vertically spaced, arcuate contactsurfaces adapted to substantially, but not quite, contact the outer wallof said cavity alternately as said core is moved in the horizontal planeof said contact surfaces; and vibration damping means adapted toyieldably support the armature and switch members from said housing.

3. A magnetically operated float switch, comprising: a housing adaptedto be hermetically sealed and having ange means for mounting the switchin a gas tank; means forming an axially disposed cylindrical cavityextending into said housing and open at its lower end; an iron coredisposed for reciprocation within said cavity; a liquid buoyant floatdisposed in substantial axial alignment below said core; a tubeoperatively connecting said core and said oat; a ventilated disc securedto said tube for guiding the lower end of the tube to maintain it insubstantial alignment with said cavity; an electrical switching meanshaving two opposed, two contact, switch members which are resilient butixedly mounted and, a movable double faced contact switch memberdisposed between the resilient members; a curved permanent bar magnetadapted to energize said switching means; a counterbalanced soft ironarmature, mounted on a horizontal pivot and disposed in the flux path ofsaid magnet; an arm secured to said armature and operatively connectedto said movable switch member; said armature having vertically spaced,angularly disposed arcuate contact surfaces adapted to come into closeproximity with the outer wall of said cavity, alternately as said coreis positioned in the horizontal planes of said contact surfaces;attaching means for fixedly securing said magnet to said housing andvibration damping means adapted to yieldably support the armature andswitch members from said housing and magnet.

4. A magnetically operated two position switch, comprising: a housingand a pair of soft iron armatures mounted in said housing freely pivotalabout two parallel, spaced apart axes, a magnetic source in said housingdisposed to form a strong ux field passing between the armatures, eacharmature being substantially balanced about its axis and said magneticsource exerting a force considerably in excess of the forces of gravityacting upon the armatures, a soft iron core member positioned in saidhousing movable between a first and a second position on a path oftravel between the armatures lateral to the plane common to said axes;each armature having its side portion adjacent said path of traveldivided into two large, independent sections and said first position ofsaid core member being closer to one section and said second position ofsaid core member being closer to the other section whereby saidarmatures pivot so that the adjacent section assumes the positionclosest to the core member, said armatures having a first electricalcontact moving therewith and there being two other electrical contactspositioned in said housing arranged so that said first contact abuts onewhen the armatures have pivoted to one position when said core member isin said first position and abuts the other when the armatures havepivoted to another position when said core member is in said secondposition; and operating means for moving said core member between itspositions thereby operating the switch.

5. The subject matter of claim 4 in which each armature has an armextending therefrom and one of said arms carries said first electricalcontact, and one of said arms having an opening therein and the other ofsaid arms having a detent positioned in said opening forming a looseconnection therebetween so that the arms move generally together.

6. A oat switch, comprising: a housing having a passageway, an externalliquid buoyant float having secured thereto a magnetically susceptiblecore disposed for movement in said passageway responsive to movement ofsaid iioat between a first and a second position along said passageway,a pair of juxtaposed counterbalanced magnetically susceptible armaturessupported in said housing alongside said passageway and each having itsface toward said passageway bifurcated forming two large face portionsseparated in a direction parallel to the axis of said passageway andeach armature being pivotally mounted to pivot between a first positionin which one face portion is closer to said passageway and a secondposition in which the other face portion is closer to said passageway,magnetic means in said housing directing a flux iiow through the area ofthe face portions of said armatures with the iiux flow being disposedand being of such strength to pivot the armatures between their iirstand second positions responsive to the movement of said core between itsfirst and second positions, the first position of said core being closerto one face portion of each armature and the second position of saidcore being closer to the other face portion of each armature whereby theux flow passes through the face portions of the armatures closest to thecore and thereby pivots the armatures toward the core, said armatureshaving linkage means therebetween so as to pivot generally together, andelectrical switching means connected to said armatures and responsive tothe pivoting of said armatures between their first and second positionsto switch contacts.

7. A float Switch, comprising: a housing having a passagen/ay, anexternal liquid buoyant oat having secured thereto a magneticallysusceptible core disposed for movement in said passageway responsive tomovement of said iioat between a first and a second position along saidpassageway, an armature supported in said housing alongside saidpassageway and having its face toward said passageway divided into twoface portions which are separated in a direction parallel to the axis ofsaid passageway and the armature being pivotaily mounted to pivotbetween a irst position in which one face portion is closer lo saidpassageway and a second position in which the other face portion iscloser to said passageway, magnetic means in said housing directing aflux iiow through the area of the face portions of said armature withthe iiux flow being disposed and being of such strength to pivot thearmature between its first and secc-nd positions responsive to themovement of said core between its first and second positions, the rstposition of said core being closer to one face portion of said armatureand the second position of said core being closer to the other faceportion of said armature whereby the iiux How passes through the faceportion of the armature closest to the core and thereby pivots thearmature toward the core, and electrical switching means connected tosaid armature and responsive to the pivoting of said armature betweenits rst and second positions to switch contacts.

8. A switch, comprising: supporting means and a magnetically susceptiblecore supported by said supporting means for movement, responsive toexternally applied force, along a path of travel between a rst and asecond position, an armature supported by said supporting meansalongside said path of travel and having its face towar said path oftravel divided into two face portions which are separated in a directionparallel to said core path of travel and the armature being pivotallymounted to pivot between a first position in which one face portion iscloser to said core path of travel and a second position in which theother face portion is closer to said core path of travel, magnetic meanssupported by said supporting means dirooting a flux ow through the areaof the face portions of said armature with the flux flow being disposedand being of such strength to pivot the armature between its first andsecond positions responsive to the movement of said core between its rstand second positions, the first position of said core being closer toone face portion of said armature and the second position of said corebeing closer to the other face portion of said armature whereby the uxow passes through the face portion of the armature closest to the coreand thereby pivots the armature toward the core, and electricalswitching means supported by said supporting means and connected to saidarmature and responsive to the pivoting of said armature between itsfirst and second positions to switch contacts.

References Cited in the file of this patent UNITED STATES PATENTS803,486 Hill Oct. 31, 1905 1,216,420 Dodgson Feb. 20, 1917 1,891,568Morris et al Dec. 20, 1932 1,958,685 Tevander May 15, 1934 2,068,093Terjesen Jan. 19, 1937 2,069,641 Bold et al Feb. 2, 1937 2,142,680Shrode Jan. 3, 1939 2,204,161 Shepherd June 11, 1940 2,467,073 BinfordApr. 12, 1949 2,544,491 Davis Mar. 6, 1951 FOREIGN PATENTS 593,315Germany Feb. 24, 1934

